An HEV (Hybrid Electrical Vehicle) runs on driving force from an internal combustion engine and/or an electric motor. FIG. 14 is a block diagram of an internal configuration of the HEV. In the HEV (hereinafter, referred to simply as the “vehicle”) shown in FIG. 14, driving force from an internal combustion engine (ENG) 107 and/or an electric motor (MOT) 101 is transmitted to drive wheels 153 via a gearbox 109 and a drive shaft 151. In the vehicle shown in FIG. 14, a rotor of the electric motor 101 is connected directly to a drive shaft of the internal combustion engine 107. Thus, when the internal combustion engine 107 runs, the rotor of the electric motor 101 also rotates.
The internal combustion engine 107 generates a driving force (an output torque) to run the vehicle. An engine ECU (ENG ECU) 117 controls the internal combustion engine 107. The electric motor 101 is a three-phase AC motor, for example, and generates a driving force (an output torque) to run the vehicle. A motor ECU (MOT ECU) 119 controls the electric motor 101. A battery (BATT) 103 is a DC power supply and supplies electric power to the electric motor 101 via an inverter 105. The output voltage of the battery 103 is a high voltage (for example, 100 to 200V). The inverter 105 converts a DC current from the battery 103 into three phase AC currents. An inverter ECU (INV ECU) 111 controls the inverter 105.
A clutch 113 interrupts or connects a transmission line of driving force from the internal engine 107 and/or the electric motor 101 to the drive wheels 153 based on an instruction from a management ECU 115. When the clutch 113 is disengaged, the driving force is not transmitted to the drive wheels 153, but the clutch 113 is engaged, the drive force is transmitted to the drive wheel 153. The gearbox 109 is a transmission which converts the driving force from the internal combustion engine 107 and/or the electric motor 101 into a rotational speed and torque at desirable gear ratios for transmission to the drive shaft 151.
The management ECU (MG ECU) 115 controls the internal combustion engine 107, the electric motor 101 and the inverter 105, instructs the clutch 113 to be engaged or disengaged and instructs the gearbox 109 to change the gear ratios thereof.
FIG. 15 is a block diagram of a driving system installed in the vehicle shown in FIG. 14 for driving the electric motor 101. As shown in FIG. 15, in the inverter 105, arms 1u, 1v, 1w are provided correspondingly with phases (U phase, V phase, W phase) of the electric motor 101, and the arms 1u, 1v, 1w are connected in parallel to a smoothing capacitor C between power supply terminals 2a, 2b. Central points of the respective arms 1u, 1v, 1w are connected to a U-phase armature Au, a V-phase armature Av and a W-phase armature Aw of the electric motor 101, respectively.
A switch unit includes a switching element such as IBGT or MOSFET and a reflux diode connected in parallel to the switching element. Such switch unit is provided on each of a positive side and a negative side on each of the respective arums. For example, for each of the respective arms, a switch unit 5a including a switching element 3a and a reflux diode 4a is provided on a positive side, and a switch unit 5b including a switching element 3b and a reflux diode 4b is provided on a negative side. On each arm, a collector of the positive-side switching element 3a and a cathode of the positive-side reflux diode 4a are connected to the positive-side power supply terminal 2a, and an emitter of the negative-side switching element 3b and an anode of the negative-side reflux diode 4b are connected to the negative-side power supply terminal 2b. A positive terminal of the battery 103 is connected to the positive-side power supply terminal 2a via a contactor SW.
Each switching element is on/off controlled by a control signal from the inverter ECU 111. Agate resistor R is connected to a gate terminal of each switching element, and a control signal from the inverter ECU 111 is inputted into the gate terminal via the gate resistor R.
When a failure is generated in which the resistance value of the gate resistor R is increased, the switching speed of the switching element becomes slow, and the switching loss is increased, whereby the temperature of the switching element is increased. As a result, a thermal runaway occurs in the switching element which may result in a short-circuit failure. Further, when the inverter 105 including the short-circuited switching element is continuously used, a greater current than the normal current flows, and therefore, the electric motor 101 or three-phase wires may fail. Consequently, in Patent Document 1, in order to prevent the occurrence of malfunction or trouble in the electric motor 101 or three-phase wires when a short-circuit failure occurs in the inverter 105, a greater current is prevented from flowing to the inverter 105.
For example, in Patent Document 1, when the switching element of the switching portion 5b to which a U-phase current flows short-circuits to fail, the inverter ECU 111 on controls the switching elements of the switching portions 5b which are provided on the negative side and off controls the switching elements of the switch units 5a which are provided on the positive side. Consequently, there is produced a state in which inverter 105 side ends of the armatures Au, Av, Aw of the respective phases of the electric motor 101 are substantially short-circuited relative to each other. Hereinafter, this state will be referred to as a “three-phase short-circuited state.” And, a control to generate the three-phase short-circuited state in the electric motor 101 will be referred to as a “three-phase short-circuiting control.” FIG. 16 shows examples of waveforms of the respective phases which are generated when the rotor of the electric motor 101 which is in the three-phase short-circuited state is rotated by driving the internal combustion engine 107.